It is well-known to mount timber-working devices, commonly referred to as forestry or harvester heads, to a carrier vehicle in order to perform a number of operations in connection with timber processing. These operations may include one, or a combination of, grappling and felling a standing tree, delimbing a felled stem, debarking the stem, and cutting the stem into logs (known as bucking) commonly using at least one chainsaw.
Feeding the stem along its length relative to the head is typically achieved using arm mounted rotary drives having a feed wheel at the end of opposing drive arms configured to grasp the stem, together with at least one frame mounted feed wheel.
It is generally desirable to have the drive arms close at the same rate in order to center them (and the stem or stems they are acting against) in the head. It is known to provide a timing link between the drive arms in order to achieve this.
However, where there is variance in the size or linearity of the stem this synchronization can lead to one of the wheels having a lesser degree of contact with the stem than the other, creating inefficiencies.